The present invention relates to liquid-vapour distribution devices for use in two-phase concurrent down-flow vessels. In particular, the invention concerns a liquid distribution tray being equipped with vapour lift tubes that improve distribution of liquid and vapour phases over the cross sectional area of a vessel beneath the tray to achieve thermal and compositional equilibrium. The device is in particular useful in hydroprocessing reactors.
The known designs of liquid distribution devices fall into one of five categories. The first is a series of troughs and overflow weirs to systematically subdivide the liquid into multiple streams before it contacts the bed. This type is often used in liquid contractors or countercurrent absorbers. An example of this type is described in U.S. Pat. No. 5,192,465.
A second type of liquid distribution device is a perforated horizontal tray. This may or may not have notched weirs around the perforations. The tray may also have chimneys for vapour flow. This type of distribution device can be used for rough liquid distribution in conjunction with a more sophisticated final liquid distribution tray. Examples of this type are disclosed in U.S. Pat. No. 4,836,989.
The third common type of liquid distribution device is a chimney tray. This device uses a number of standpipes laid out typically on a regular square or triangular pitch pattern on a horizontal tray. The stand pipes typically have holes in the sides for the passage of liquid. The tops of the standpipes are open to allow vapour flow down through the centre of the chimneys. Some designs use special vapour downcomer chimneys to handle the bulk of the vapour flow. This type is known from U.S. Pat. Nos. 4,126,540 and 3,353,924.
The fourth type of liquid distribution device is a bubble cap tray. This device uses a number of bubble caps laid out on a regular-pitched pattern on a horizontal tray. The bubble cap is formed with a cap centered concentrically on a standpipe. The sides of the cap are slotted for vapour flow. Liquid flows under the cap and, together with the vapour, flows upward in the annular area and then down through the centre of the standpipe as described in U.S. Pat. No. 5,158,714.
A further known type of liquid distribution device is perforated tray provided with vapour lift tubes in form of a long legged downcomer fitted with one or more short legged upcomers creating an up-flow zone and down-flow zone within the tube. The sides of the short legged upcomer are slotted in the vapour lift tubes, liquid flowing concurrently with vapour is lifted by means of the vapour flow upwardly in an up-flow zone and evenly distributed together with the vapour through the down-flow zone to an underlying catalyst bed as further described in U.S. Pat. No. 5,942,162.